794 Proceedings of the Royal Society 
curves of salinity obtained at Alloa on April 28 are shown on Plate 
XXVIII. fig. 6. 
At Kincardine there was always a more marked change in salinity 
with depth, and while at high water there was a minimum differ- 
ence between surface and bottom, and a nearly uniform vertical 
distribution, in the early part of ebb the greater part of the increase 
of density was in the first fathom, and in the early part of flood in 
the fathom nearest the bottom. The travelling downward of the 
point of inflection in the curve corresponding to the increasing fresh- 
ness of the upper strata of water as the tide falls is shown clearly 
in diagram 5, Plate XXVIII. 
Observations of Temperature. 
The relation of the temperature of the water to its salinity was 
such at the time of our observations that surface water which 
was fresher was also warmer than that at the bottom, and water 
from the upper part of the estuary was warmer than that in the 
lower part. It thus happened that an increase of salinity was 
always accompanied by a decrease of temperature, and a decrease of 
salinity by an increase of temperature. It will be seen, by refer- 
ence to Plate XXVIII. figs. 5 and 6, that the curves illustrating the 
vertical distribution of temperature in the water at any time were 
almost mirror images of those representing density. The position 
and amount of inflection in the corresponding curves are, in fact, 
the same, though the directions are opposite. It thus appears that 
at this season of the year the thermometer alone is sufficient to 
trace out the interaction of the frithial and fluvial water in such an 
estuary as that of the Forth. The following notes, although taken 
from individual cases, illustrate what we found to be the conditions 
characteristic of the various phases of tide during the period of our 
observations. The range of temperature for the whole time was 
rather less than 5° F., varying from 50° to 45 0, 5, and the difference 
between surface and bottom rarely amounted to so much as 3°, 
Ebb Tide . — Kincardine : depth of water, 3 to 5 fathoms. From 
one to three and a half hours of ebb the vertical distribution of tem- 
perature remains practically the same, being nearly uniform from the 
bottom to about 4 feet from the surface, where there is a sudden 
increase in the rate of rise. The temperature of the whole mass of 
